Deworming
Do We Have To Talk About This Again?

Written by: Dr. Jay Altman

Deworming is one of the most important components of any equine preventative healthcare programs. Due to the fact that the internal parasites can build resistance, and manufacturer's products change, there are many product options and numerous recommendations offered in various different publications, and the topic is worthy of regular review.

Most readers understand that it is important to deworm their horses. But with the talk of many different internal parasites, 20 or so dewormers on the market, and at least two dozen different "recommended" deworming programs, many of our clients are still in a quandary as to the best program and products for their horse. In this column, we will address some of the basics of who, how, what and when.

Every horse starting at about 4 weeks of age needs to be dewormed on a regular basis. Deworming products come in various different forms, all of which are administered orally. The dewormers can be administered either in the feed, directly in the mouth, or via nasogastric tubing. Every one of the modern deworming compounds comes in at least a paste or gel form for simple owner oral administration. For horses that are difficult to "paste", you can consider looking for the "top dress" feed additive forms of the chemicals. Although some chemicals are available this way, not all are, and so if pastes are a problem for you to administer, you will need to work with a modified program and may need the help of your veterinarian to administer some of the products or to guide you in a modified program. Therefore, the two large questions that remain are when to deworm, and with what product.

There are four major scheduling schemes; interval, daily, seasonal and demand. Interval deworming is the practice of deworming based upon a predetermined time frame, most commonly either every 60 or 90 days. Daily deworming programs involve the administration of a feed additive of low dose dewormer (pyrantel tartrate) with the addition of multiple purge dewormings (oral paste or gel), either two or three times per year. Seasonal deworming programs can be quite variable in nature and as it sounds they are tied to the change of the seasons. The two major changes come as winter and summer, and so these programs can be quite flexible and depending upon the person designing the program, can be comprised of between two and four dewormings per year. Demand or as needed programs are based upon the collection and analysis of fecal samples, the deworming frequency, and the type of deworming product being dictated by the results of multiple fecal analyses performed throughout the year.

So which is the best schedule and/or system? There is no right answer to that question. The fact is that for different management situations, different horse populations, and different budgets, any one of these four systems might be the "right" answer. Our typical recommendations are that people either use the interval method or the daily method. We rarely make recommendations that are based upon a seasonal timing, due to the variable nature of this system and that in most situations horses need more frequent deworming with a wider variety of products than the seasonal program recommends. The demand system is one that we only use in specific medical situations, and although it can be an excellent program, its implementation is both time consuming and costly.

What to use is the next issue that most people face. If you are on a daily deworming product then your main product is the daily feeding of pyrantel, in addition to this product the recommendation is for either two or three purge dewormings per year. For these horses we recommend three purge dewormings in addition to the daily feed additive product. The three added purge dewormers are 2 ivermectin dewormings and one moxidectin with Praziquantel deworming.

For those on an interval deworming schedule we recommend rotation of products. The timing of these products is important to optimize the program's effectiveness. We currently recommend rotating between ivermectin, pyrantel, fenbendazole, oxibendizole, and moxidectin and Praziquantel products, by rotating these products in the correct sequence we can attempt to eliminate all the different species of internal parasites in the horse, while avoiding the problem of parasite resistance that might be caused by using a single product multiple times.

Additionally, we recommend that an annual fecal sample be collected and analyzed to test the efficacy of both the scheduling of, and the products we have selected. We also urge good management practices, which includes pasture management and manure disposal.

Our recommendation for an interval-deworming program for both adults and foals are included below. For horses just entering your care, and with either an uncertain deworming history, or a history of infrequent deworming, we recommend beginning your deworming program with a Panacur Power Pack, which is a 5 consecutive day double dose of fenbendazole. It is sold in a convenient package comprised of 5 double volume tubes. For horses that are debilitated and/or thin, and for pregnant mares, we recommend that you speak to us before settling on any deworming program. Note that we do not recommend using any product containing moxidectin in horses that are underweight or under 1 year of age.